Transformer



PATENTED FEB. 16, 1904.

G. B. MOGURDY.

TRANSFORMER.

APPLIGATION FILED APR. 24. 1902.

N0 MODEL.

M P MW \1 Q i i WW 'J'\/ i i WITNESSES INVENTOR 7M Auk/am UNITED STATES Patented February 16, 1904.

PATENT OFFICE.

CHARLES B. MoCURDY, OF WARREN, OHIO, ASSIGNOR, BY DIRECT AND -MESNE ASSIGNMENTS, TO THE PEERLESS ELECTRIC COMPANY, OF WARREN, OHIO, A CORPORATION OF OHIO, AND FREDERICK C. SUTTER AND ROBERT V. BINGAY, OF PITTSBURG, PENNSYLVANIA.

TRANSFORMER.

SPECIFICATION forming part of Letters Patent No. 752,405, dated February 16, 1904.

Application filed April 24, 1902.

T0 aZl whom it may concern.-

Be it known that I, CHARLEs B. MoCURDY, of Warren, in the county of Trumbull and State of Ohio, have invented a new and useful Improvement in Transformers, of which the following is a full, clear, and exact description, reference being had to the accompanying drawings, in which- Figure 1 is a diagrammatic View of my improved transformer adapted to a three-wire system, and Fig. 2 is a similar view illustrating a modification of my invention in which the voltage of the secondary coil is changed.

My invention consists in certain new and useful improvements in alternating-current transformers, intended for use in connection with a three-wire system or with systems using more than three wires, in which substantially normal regulation is maintained under balanced or unbalanced loads.

Transformers with a single magnetic circuitthe core type, commonly so calledas usually constructed are unsuited for use with a three-wire system for the following reasons: When the loads on the various branches are unequal in amount the regulation or drop in voltage shown by the transformer will appear abnormal. The normal drop or regulation of a transformer is that drop or regulation appearing when the transformer operates with its secondary winding connected to the simple two wire system. When, however, the ordinary form of coretype transformer, in which there are two primary coils, one upon each leg of the core and connected in series in manner shown in my drawing of my improved transformer, and two secondary coils, one upon each leg of the core, is connected to a three-wire system, a new element enters into its operation which causes the regulation or drop in voltage to differ very materially from that which the same transformer will exhibit when carrying similar loads on a two-wire circuit. This new element is not a constant, and its effect on the regulation varies with the distribution of the Serial No. 104,426. (No model.)

load between the various branches of the three-wire system. It has been observed that when the load is equally distributed between the two branches of the three-wire circuit the disturbing effect vanishes and the regulation or drop in voltage is normal. When one side of the three-wire circuit is fully loaded and the other side is carrying no load, the maximum disturbing effect appears. Under these conditions the drop in voltage across the loaded branch will be five or six times the normal voltage drop, and at the same time the voltage across the unloaded branch will increase a corresponding amount. For example, such a transformer supplying a threewire system with one hundred volts normal difference of potential between the outer wires and the middle or neutral wire will under the above n1aximum-disturbing effect exhibit a voltage of approximately eighty-five volts across the loaded branch and a voltage of one hundred and fifteen volts across the unloaded branch. The disturbingefi'ect willvary from this maximum up to zero when the load is evenly distributed, and it is thus evident that such a transformer is entirely unsuited to the commercial distribution of light and power. The immediate cause of such voltage fluctuations is a distortion of the magnetic field. This distortion is of such a nature that a portion of the magnetic flux is shunted around the secondary coil which supplies current to the loaded branch of the three-wire system, and at the same time this portion of the flux seems to be added, to that portion of the flux which passes through the secondary coil supplying current to the lightly-loaded branch. In order, therefore, to prevent such abnormal variations, it is necessary that the transformer be so constructed that no appreciable distortion of the magnetic field can exist under any distribution of load between the various branches of the circuit.

One of the earliest laws recognized in transformer design and construction is that the primary and secondary coils must be so 10- cated with reference to each other that all of the magnetic lines of force generated by the primary winding shall pass through the secondary winding. A transformer improperly constructed, so that on account of the reaction of the secondary winding upon the primary some portion of this. magnetic flux does not pass through the secondary winding, exhibits a drop in voltage depending upon the amount of flux thus diverted. In recognition of this law it has long been customary to locate the secondary winding as closely as possible to the primary winding. In constructing a coretype transformer a new condition obtains. It will be observed that when the core-type transformer as commonly constructed is connected to a three-wire circuit the current for one branch is supplied by one secondary coil located upon one leg of the core and the current for the other branch is supplied by the remaining secondary coil which is located upon the opposite leg of the core. It is therefore readily seen that in such a transformer one of the secondary coils, although closely associated with that portion of the primary located upon its leg of the core, yet it is not so closely located to that portion of the primary which is located upon the opposite leg of the core, and the same holds true with the other secondary coil. In my approved transformer I have so arranged the secondary windings that they are closely associated with the primary windings, thus preventing distortion of the magnetic field and consequent fluctuation in voltage, as above described. Considering, therefore, the commonly-constructed core-type transformer connected to a threewire circuit it will be observed that when one branch of the three-wire circuit is more heavily loaded than the other branch there will be a greater current flowing through the secondary coil upon one leg of the core than there is flowing through the secondary coil upon the opposite leg, and in its electrical arrangement the transformer is thus unsymmetrical.

In my improved transformer (illustrated in Figs. 1 and 2) the primary windings 5 and 6 are arranged in the same manner as in the common form of transformer above described. The secondary winding of my transformer, however, is so arranged upon the core that the portion which supplies any one branch of the three-wire system is located partly upon each leg of the core and is thus closely associated with all of the primary winding.

A further object of my invention is to provide a system in which the voltage of the secondary coil may be changed, and this I accomplish by cutting in or out a certain number of turns of the secondary coil.

In the drawings, referring to Fig. 1, 2 and 3 represent the main wires, and 4 is a trans former, which is provided with two primary coils 5 and 6, these coils being connected to the main wires 2 and 3. These coils 5 and 6,

in a similar manner.

together with the secondary coils 7 and 8, are

wound around the legs 9 and 10 of the transformer 4E. The secondary coils 7 and 8 are wound in opposite directions to each other and are connected together in multiple. The coils 7 and 8 have a tap 11 brought from the center of each to be connected directly between said coils, so as to form the central or neutral wire necessary in a three-wire system. By employing this system of winding of the secondary coils each coil is wound to give the full potential of the secondary circuit, and by thus forming the winding of the secondary coils a balanced winding for an unbalanced load is effected without the multiplication of the parts or complication of the circuits.

Again referring to Fig. l of the drawings, it will be seen that a portion of the secondary coil 7 is connected in multiple with a portion of secondary coil 8, these two portions supplying current to one branch of the three-wire circuit. It will be seen, further, that the remaining portion of secondary coil 7 is conneeted in multiple with the remaining portion of secondary coil 8, these two portions supplying current to the other branch of the threewire circuit.

Considering now the ease of an unbalanced load upon my improved transformer and assuming that one branch of the three-wire circuit is carrying a greater load than the other branch, it will be seen that the greater load is divided equally between the two portions of the secondary windings which are located upon opposite legs of the core and which are supplying current to the heavily loaded branch, and, again, it will be seen that the lighter load of the other branch of the threewire circuit is divided equally between the other two portions of the secondary winding The sum of the currents in the secondary windings located on one leg of the core is thus equal in amount to the sum of the currents in the secondary windings which are located on the opposite leg of the core, and electrically considered the transformer is symmetrical regardless of the fact that the load is unequally distributed between the branches of the three-wire system.

My transformer may be applied to a circuit of more than three wires and a similar arrangement of coils adopted to secure immunity from unbalancing effect.

If desired, my transformer may be reversed when the supply-mains are arranged in a threewire system and the service-mains are arranged in a two-wire system, in which case the supply-mains would be connected to what has been above explained as the secondary winding and which would now become the primary winding and the service-wires would be connected to what was the primary windings, which would now become the secondary windings.

Referring to Fig. 2 of the drawings, I illus trate a modification of my transformer with respect to the secondary windings, in which a multiplicity of taps 11 are taken from the sec ondary coils, so that by cutting in or out any given number of turns in the secondary coils, and thus changing the ratio of the windings, a variation in the voltage of the secondary circuit is accomplished. In all other respects the transformer is the same as described in Fig. 1. By employing a transformer in which the voltage of the secondary coils may be changed, as just described, the same transformer may be used through a wide range in voltage, if necessary, such construction doing away with the necessity of employing different transformersfor example, in making tests of different kinds.

The advantages of my invention will be apparent to those skilled in the art, since I am enabled without complication of the device or the electrical circuits employed to obtain a transformer which shows practically normal regulation under all conditions of load and in which each secondary coil gives the full potential of the secondary circuit and in which by leading from the secondary coils one or more taps the desired voltage may be obtained without increasing the number of parts of the apparatus or the complication of the circuits.

Modifications of my invention will suggest themselves to the skilled electrician, and changes in form and arrangement of the parts may be made without departing from my invention, since I claim 1. In a transformer, the combination of a core having a single magnetic circuit; a primary winding consisting of two coils, one coil on each leg of said core; a secondary winding upon said core, consisting of two coils, one upon each leg, one secondary coil being wound reverse or opposite to the other; each secondary coil having a tap from its center, said taps being connected between said coils to form the neutral wire for a three-wire system, substantially as described.

2. The combination, in a transformer, of a core having a single magnetic circuit, a primary winding mounted thereon, a secondary winding mounted thereon, consisting of two coils, one coil being wound reverse or opposite to the other, said coils having a tap brought from the center of each, said taps being connected directly between said coils to form the central or neutral wire necessary for a three- Wire system, thus forming a balanced winding for an unbalanced load, which will show practically normal regulation under any condition of unbalanced load.

3. In a transformer, the combination of a core having a single magnetic circuit, a primary and secondary winding mounted thereon, consisting of two or more sets of two coils each, one coil of each set being located on each leg of said circuit, one secondary coil being wound reverse or opposite and having taps brought out at convenient parts of said coil, said taps to be used as means of changing or varying the voltage of the secondary circuit by cutting in or out any given number of turns in the secondary coil, thus changing the ratio of the windings.

4. The combination in a transformer, of a core having a single magnetic circuit, a primary windingmounted thereon, and a secondary winding mounted on said core consisting of two or more groups of coils connected to a three-wire system, there being an equal number of groups connected across each branch of the three-wire system, each of said groups consisting of two or more coils located on different parts of the core, and connected in multiple across the branch of the three-wire system to which said group pertains.

5. The combination in a transformer, of a core having a single magnetic circuit, a primary winding mounted thereon, and a secondary winding consisting of two sets of coils connected to a three-wire circuit, one set being connected across one branch and the other set across the other branch of the three-wire circuit, each of said sets being composed of two coils connected in multiple, one of said coils being located on one leg of the core and the other coil located upon the other leg of said core.

6. In a transformer, the combination with a core constituting a single magnetic circuit, of a winding disposed at different parts of the core, a portion of the winding on one part of the core being connected in multiple with a portion of the winding on another. part of the core, across one side of a multicircuit system, other parts of the winding on different parts of the core being connected in multiple with each other across another side of a multicircuit system, and another winding in inductive relation with respect to the first winding.

7. The combination in a transformer, of a core having a single magnetic circuit, a primary winding mounted thereon, and a secondary winding consisting of two portions, one portion being connected across one branch of a three-wire circuit and the other portion being connected across the other branch of said three-wire circuit, each of which portions is composed of two parts connected in multiple one part being located upon one leg of the core and the other part being located upon the opposite leg of the core.

In testimony whereof I have hereunto set my 

